The present invention relates to a cam device (for example, a positive cam) including a rotatable cam follower (for example, a roller) moving along a groove.
U.S. Pat. No. 6,073,503 discloses a cam device comprising a cam, a follower and elastic member for causing the follower to follow the cam. This type of cam is not suitable for high-speed movement.
FIG. 6 shows a positive cam of the type described above. As shown in FIG. 6, a cam follower 200 tends to be rotated in opposite directions when it is in contact with a first sidewall 101 of a cam groove 100 and when it is in contact with a second sidewall 102 thereof. To state more specifically, when the cam follower 200 moves relatively in the direction shown by arrow X along the cam groove 100, at a first position P1, the cam follower 200 moves forward while rotating clockwise keeping contact with the first sidewall 101. At a second position P2, however, the cam follower 200 moves forward while rotating counterclockwise keeping contact with the second sidewall 102.
Since the direction of the rotation of the cam follower 200 is reversed during the movement from the first position P1 to the second position P2, the cam follower 200 experiences sliding contact without rolling during this movement. The degree of friction due to sliding contact is markedly great compared with that due to rolling contact, and this sliding friction is noticeable when the cam follower moves at high speed.
An object of the present invention is to provide a cam device superior in durability with reduced friction.
In a first aspect of the present invention, in a cam device including a rotatable cam follower performing predetermined movement along a groove defined by first and second sidewalls, the cam follower includes individually rotatable first and second cam followers, and these cam followers are placed so that their axes extend in the same direction. Movement of the first cam follower is restricted by at least part of the first sidewall, and movement of the second cam follower is restricted by at least part of the second sidewall.
In a second aspect of the present invention, in a cam device including a rotatable cam follower performing predetermined movement along a groove defined by first and second sidewalls, the cam follower includes individually rotatable first and second cam followers, and these cam followers are placed so that their axes extend in the same direction. The first sidewall has a portion protruding toward the center of the groove, and the second sidewall has a portion protruding toward the center of the groove.
According to the first and second aspects of the present invention, the first cam follower is in contact with the first sidewall. Therefore, theoretically, the rotation direction of the first cam follower is prevented from changing even when the orientation of the cam changes in direction. Likewise, since the second cam follower is in contact with the second sidewall, the rotation direction of the second cam follower is theoretically prevented from changing even when the orientation of the cam changes in direction.
The first cam follower may come into contact with the second sidewall, or vice versa, for a brief period of time due to a disturbance (for example, due to an attaching of foreign matter and dirt). In such a case, however, since the first cam follower is prevented from rotating in reverse, the wear is small and thus the life of the cam device is prolonged.
According to another aspect of the present invention, the two cam followers are placed in one groove. Preferably, at least one of the sidewalls of the groove includes a lower sidewall face and an upper sidewall face, and these sidewall faces are displaced from each other with respect to the center of the groove.
Preferably, the two cam followers share the same rotation axis, that is, they are placed or situated coaxially. As the construction enabling the two cam followers to rotate individually, the first cam follower and/or the second cam follower preferably have a ball bearing or a roller bearing.
The first and second cam followers may be the same or different in thickness. In particular, one of the cam followers that wears more easily may be made thicker than the other cam follower. Alternatively, one of the cam followers that wears more easily may be made of a material more rigid (for example, higher in wear resistance) than the other cam follower. Otherwise, the wear of the two cam followers may be made uniform by performing a surface treatment, and such uniformity ensures constant outer-diameters of the first and second cam followers.
The first and/or second cam followers may have a barrel-shaped circumference.
Examples of the positive cam to which one of the present invention is applicable include cylindrical cams, columnar cams, conical cams, spherical cams, and face cams.